Ditcher for permafrost

ABSTRACT

In a ditcher having a horizontal main frame, upstanding suspension frame, and wheel frame suspended from the suspension frame, means are provided for tilting the wheel frame relative to the main frame so that the ditching wheel supported by the wheel frame may be held vertical, even when the machine is operating on a side hill. Said means comprise two parallel, spaced cylinders, extending downwardly from the suspension frame to the wheel frame, having spherical bearings for connection to the frames; the cylinders, when adjusted to uneven length, tilt the wheel frame relative to the main frame. Hydraulic cylinder means are also provided to exert a downward force on the wheel frame to press the wheel into hard ground and hold it in the lowered position.

United States Patent [1 1 Bartels 1 Feb.4,1975

[ DITCHER FOR PERMAFROST [73] Assignee: Banister Continental Ltd.,

Edmonton, Province of Alberta, Canada [22] Filed: Mar. 20, 1973 [21]Appl. No.: 343,107

Primary Examiner-Ernest R. Purser Attorney, Agent, or FirmMillen, Raptes& White [57] ABSTRACT In a ditcher having a horizontal main frame,upstanding suspension frame, and wheel frame suspended from thesuspension frame, means are provided for tilting the wheel framerelative to the main frame so that the ditching wheel supported by thewheel frame may be held vertical, even when the machine is operating ona side hill. Said means comprise two parallel, spaced cylinders,extending downwardly from the suspension frame to the wheel frame,having spherical bearings for connection to the frames; the cylinders,when adjusted to uneven length, tilt the wheel frame relative to themain frame. Hydraulic cylinder means are also provided to exert adownward force on the wheel frame to press the wheel into hard groundand hold it in the lowered position.

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' sum user 11 PAIENIED FEB 4 I975 SHEET 10 0F 11 PATENIED 41975 3868888sum 110? 11 DITCHER FOR PERMAFROST BACKGROUND OF THE INVENTION Thisinvention relates to a ditcher of the type used to excavate pipelinetrenches and the like.

A conventional ditcher generally comprises a carrier, usually a crawlertractor, carrying a rotatable digging wheel at its rear. Moreparticularly, the carrier supports an upstanding, rigid suspensionframe. This suspension frame includes one or two substantially verticalbeams at its rear end. Each vertical beam carries a slide guide. Thedigging wheel is held in a rigid wheel frame, which is generallyrectangular in shape and extends around the wheel. The front end of thiswheel frame is pivotally attached to a slide member. In turn, the slidemember is mounted on the beam slide guide and can slide up and downthereon to alter the elevation of the wheel. A substantially verticalhydraulic cylinder is suspended from the upper end of the suspensionframe and is attached at its lower end to the slide member. Contractionand expansion of this cylinder moves the wheel frame between theelevated travelling position and the lowered digging position. A cableis attached to the rear end of the wheel frame. It entends over asheave, carried by the suspension frame, to a drum on the carrier. Thiscable functions to suspend the wheel frame horizontally when the ditcheris digging a trench. It also serves to rotate the wheel frame upwardly,about its front pivot connection, to the elevated travelling position.The tractor is equipped with a motor, and suitable hydraulic systems anddrives for operating the digging wheel and actuating the liftingcylinders. It will be noted that the conventional ditcher in use todayrelies on the sheer weigh ofthe digging wheel to obtain penetration intothe soil although it has been suggested by others that the cable may bereplaced with a hydraulic cylinder to force the wheel down (see US. Pat.Nos. 3,226,856 and 3,510,970).

At the present time there is a need for a ditcher which can operate inthe Arctic to excavate trenches for the laying of large-diameterpipelines. Existing ditchers are not suitable for this service, as willbe rec ognized from the following discussion.

Many areas of the Arctic are covered with permafrost. This a hardmixture of ice and organic material, such as peat. The permafrost mayextend from a depth of several feet to several thousand feet. At itssurface, the permafrost is frequently covered with a surface mat ofvegetation, such as grass or lichen. This surface mat may vary inthickness from a few inches to a foot or more. In summer, the surfacemat insultes the permafrost from the heat of the Arctic sun. If thesurface mat is not present, the permafrost will, of course, melt in thesummer. An example will serve to bring out the seriousness of thisthermal erosion problem: A trench having a width and depth of one foot,and length of twenty feet was cut into the permafrost about five yearsago. Today this trench has a width of about twenty feet, a length ofserveral hundred yards, and a depth of approximately 50 feet.

ln pipeline practise, it is necessary to excavate a trench having alevel bottom. Otherwise the pipe will lie against the wall of thetrench, which is undesirable. It is therfore conventional to precede theditcher with a bulldozer which cuts a level right-of-way across sidehills and the like. This practise is unacceptable for the Arctic, as thesurface mat will be removed. It is possible to replace a strip of mathaving a width of a few feet with wood chips however it is impracticalto do this across a width of approximately twenty feet. In any case, thepermafrost is so hard that a bulldozer cannot shave it down in areasonable period of time.

With the foregoing comments in mind, it is one object of this inventionto provide a ditcher having the combined capabilities of being able to:(1) force the digging wheel into the hard permafrost and hold it therewhile trenching; and (2) tilt the digging wheel, when the ditcher isoperating on a side hill, so that the trench walls are always verticaland its bottom is horizontal.

As described below, hydraulic cylinders or their mechanical equivalentsare preferably used in this invention to hold the wheel frame and itsassociated wheel in place so that this wheel assembly cannot ride up outofthe trench when operating in hard permafrost. There is a a liklihoodthat the wheel will periodcially encounter particularly hard materialwhen digging and, if rigidly connected to the hold down cylinder, itwill exert excessive forces on the cylinder, eventually damaging it. inaddition in passing over bumps in the hard terrain, verticalmisalignment will occur between the carrier and the digging wheelassembly, thereby also creating a strain on the hold down cylinder.

It is therefore another object of this invention to provide a limitedamount of play" or float capability at the connection between the holddown cylinder and the wheel frame so that, while the cylinder doesconstrain the wheel frame substantially in the digging position, alimited range of movment of the wheel frame about its pivot connectionwith the suspending frame is still permitted. This play serves anotherfunction, as explained bleow, in that it makes it possible to tilt thewheel frame.

The Arctic ditcher is required to excavate a uniquely large trenchthrough extremely hard material. With this in mind, it is another objectof the invention to provide a ditcher which is powered by twin enginesone of which drives the digging wheel only while the other engine drivesthe remaining hydraulic components. In this manner, the power availableto the digging wheel is not diminished due to periodic heavy loadconditions affecting other parts of the machine.

The ditcher is called on to operate under extremely severe weatherconditions. Temperatures below 60F are not uncommon. Under theseconditions, the frequency of mechanical breakdown is enormouslyincreased. It is therefore another object of this invention toincorporate an emergency cross-over system into the hydraulic circuitryof the machine so that, in the event that one engine breaks down, theother engine can take over sufficient functions to enable the ditcher tolift its wheel, move off the right of way, and return to the base campfor repair, or continue operating at a reduced production rate.

It is another object of the invention to provide a ditcher having anengine hydraulic circuit system which can be warmed up without load onstarting the machine.

The carriers tracks must be capable of bracketing the wide trench whichis excavated yet the carrier should still be capable of being loaded ona conventional truck bed. It is therefore another object of theinvention to provide a carrier having tracks which can be spread apartor brought together, even when the machine is standing on the ground.

It is another object of the invention to provide a ditcher having adigging wheel drive which is designed to reduce the high-stress inputbetween the sprocket and wheel segment teeth, thereby reducing theliklihood of a failure at low temperatures due to brittleness of themetal.

It is another object to provide a ditcher having a braking system toenable it to operate successfully on down-hill terrain.

It is another object of the invention to provide the digging wheelbuckets with teeth whose digging angle is substantially greater thanthat of conventional ditchers, thereby improving the excavating rate toa surprising extent.

SUMMARY OF THE INVENTION In accordance with one aspect of the invention,a ditcher is provided having the dual capabilities of being able toexert a hold down force on the wheel frame and to tilt the wheel framerelative to the plane of the main frame of the carrier. Thesecapabilities make it possible for the ditcher to trench in hard materialand to excavate a vertical trench when moving across a side hill.

According to the preferred form of the invention, a pair of spaced,parallel, independently operable lifting cylinders are suspended attheir upper ends from the rear upper section of the suspension frame. Attheir lower ends, these cylinders are connected by spherical bearingcouplings to the front end of the wheel frame. A pair of spaced,parallel hold down cylinders are connected at their front ends byspherical bearing couplings to the rear upper section of the suspensionframe. At their rear ends, the hold down cylinders are connected byspherical bearing couplings to slide structures, oflimited length, eachslide structure being associated with one side of the wheel frame.Preferably these slide structures each comprise apin, attached to thecylinder end, transversly disposed in a short slot formed in the wheelframe. Each slot extends longitudinally substantially parallel to thelongitudinal axis of the wheel frame. It will be seen, therefore, thatthere is a solid connection between each hold down cylinder and thewheel frame when the pin is at either end of the slot; yet there is abuilt-in float capability in that the pins can slide back and forthwithin the short slots. In operation, the wheel frame can be lifted orlowered by expanding or contracting the two sets of cylinders. To tiltthe wheel frame, the lifting cylinders are actuated to make them unevenin length. The spherical bearing couplings enable the joints affected bytilting of the wheel frame to accomodate the movement. The slots enablethe tilting movement to take place, even though the lengths ofthe holddown cylinders are not adjusted. In other words, as tilting takes place,there would be a jamming effect if the equally long hold down cylinderswere rigidly attached to the wheel frame. The slots or slide solve thisdifficulty by permitting limited relative movement between the wheelframe and the hold down cylinders. The slots also function to accomodateminor vertical misalignments between the carrier and the wheel assembly,as will occur when the machine is passing over undulating terrain. Thehold down cylinders can be engaged to restrain the wheel frame fromrotating about it pivot connection with the suspension frame and can beactuated to press the wheel assembly into the ground.

Broadly stated, the invention is an improvement on a ditcher comprisinga carrier, having a main frame and an upstanding suspension frameconnected with said main frame, and a rigid wheel frame, supporting arotatable ditching wheel, pivotally connected at its front end to thesuspension frame and movable thereon between a lowered position and anelevated position. The improvement comprises the combination of: meansfor rasing and lowering the wheel frame along the suspension frame;means, associated with the wheel frame and suspension frame, for tiltingthe wheel frame relative to the plane of the main frame; and means,associated with the wheel frame and suspension frame, for controllablyrotating the wheel frame downwardly about its pivot connection with thesuspension frame, to force the ditching wheel into the ground, and forconstraining it there.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a general arrangment sideelevation view of the ditcher depicting both the twin-engine powersystem and the wheel assembly shown in the digging position and in thetransport position in phantom lines.

FIG. 2 is a top plan view of the carrier, with parts removed to show thedetail of part of the track adjusting system.

FIG. 3 is a front view showing a portion of the carrier with the trackadjusting system in place the phantom lines show the adjustmentcapability of the track system.

FIG. 4 is a rear elevation showing the hoisting-tilting assembly mountedon the carrier.

FIG. 5 is a view similar to that of FIG. 4, showing the carrier in aside-hill position, with the assembly in the tilted position.

FIG. 6 is a front view, in section, of the spherical bearing means usedin conjunction with the ditcher.

FIG. 7 is a schematic hydraulic circuit system of the ditcher.

FIG. 8 is a top plan view of the ditcher.

FIG. 9 is a side elevation of the ditcher.

FIG. 10 is a perspective view showing the trackspreading system.

FIG. 11 is a side elevation, with parts broken away, depicting the drivesprocket wheels and the segment drive of the digging wheel.

FIG. 12 is an end view, with parts broken away, showing the doublesegment drive for the wheel and the drive sprockets.

FIG. 13 is a top plan view, with parts broken away, of the wheel drivesystem.

FIG. 14 is a perspective view of the hoisting-tilting assembly.

FIG. 15 is a top elevation showing the spherical bearing connection ofthe hold down cylinder with the slot member.

FIG. 16 is a side elevation showing the connection of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENT In general, the ditchercomprises a carrier A having a wheel assembly B suspended therefrom. Thecarrier, extending substantially parallel to the ground surface, A has ahorizontal main frame I to which is rigidly secured an upstandingsuspension frame 2. The main frame 1 includes the track assembly C shownin FIG. 10. This track assembly C comprises extendable transversemembers 9, and longitudinally extending track frames 90, which supportthe track system. Hydraulic cylinders 44 are provided to extend andretract the track frames 90. Front and rear engines l2, 13 are mountedon the main frame 1 and drive the various hydraulic circuits describedin detail below. A reservoir tank 23 supplies hydraulic fluid to thecircuits. The wheel assembly B comprises a wheel frame 25. This wheelframe 25 carriers a sub-frame 109, equipped with rollers 37, andsprocket wheels 38. The digging wheel 33 is rotatably mounted on therollers 37 and sprocket wheels 38. At its front end, the wheel frame 25is pivotally attached to slide members 28. These slide members 28 movealong slide rails 101 carried by the rear beams 8 of the suspensionframe 2. Lifter cylinders 27 connect the suspension frame with the wheelframe 25 and function to raise and lower the latter. Hold down cylindersconnect the upper section of the suspension frame 2 with the rear end ofthe wheel frame 25 they function to force the digging wheel into theground and hold it in place.

The Hoisting-tilting Assembly This assembly is shown isolated in FIG. 14and appears in FIGS. 1, 4, 5, and 9. It includes the upstandingsuspension frame 2 which, in the embodiment shown, is rigidly secured tothe main frame 1. The frame 2 includes a pair of substantially vertical,parallel, spaced slide beams 8. Each beam 8 includes an integral sliderail 101 positioned on its rear face. A horizontal cross bar 102connects the slide beams 8 at their upper ends. The truss members 3, 4,5, 6, 7 complete the structure. Functionally, the frame 2 provides anupward extension, of the carrier A, from which the wheel assembly B issuspended and on which in can slide between digging and travellingpositions.

A pair of spaced, parallel lifting cylinders 27 are attached at theirupper ends by trunnion joints 89 cross bar 102, which forms part of theupper rear portion of the suspension frame 2. The cylinders 27, as willbe brought out in the description of the hydraulic system which followsbelow, are adapted to be independently linearly contracted or expandedbetween fully open and fully closed positions and locked at any positionintermediate said positons.

The wheel frame 25 is pivotally connected at its front end to thesuspension frame 2. This wheel frame 25 is generally rectangular inform, being comprised of side beams 24 and cross beams 24a weldedtogether to form a rigid unit. A pair of ears 29 extend forwardly fromthe front corners of the wheel frame 25. Each of these ears 29 isconnected by first coupling means to the lower end of one ofthe liftingcylinders 27. The first coupling means comprises a slide member 28, afirst spherical bearing means 105 connecting the car 29 to the slidemember 28, and a second spherical bearing means 106 connecting the slidemember 28 to the cylinder 27. Each slide member 28 is connected to aslide rail 101 and is movable thereon.

As shown in FIG. 6, each sperical bearing means comprises a sphericalbearing and the conventional attachment means.

A bracket member 32 is firmly attached to each side of the wheel framesupper section 26. A slot 40, having end faces 106, is cut in each member32. The slots 40 extend longitudinally substantially parallel to thelongitudinal axis of the wheel frame 25.

A pair of spaced hold down cylinders 30 are attached at their rearwardends to the bracket members 31 by third coupling means. Each thirdcoupling means comprises a pin member 41 and a fourth spherical bearing.Each pin member 41 extends into the adjacent pair of slots 40 and canslide back and forth within them. At their forward ends, the cylinders30 are connected to the brackets 31 at the upper end of the suspensionframe 2 by second coupling means, namely the third spherical bearingmeans 108.

From the foregoing it will be understood that the lifter cylinders andtheir connections provide means, connecting the wheel frame andsuspension frame, for positively raising and lowering the wheel framealong the suspension frame. The operative lifter cylinders cooperatewith the spherical bearing connections to provide means for tilting thewheel frame relative to the plane ofthe main frame. The operative holddown cylinders and their connections can be engaged to provide means forcontrollably rotating the wheel frame downwardly about its pivotconnection with the suspension frame to force the digging wheel into theground, or locked to constrain the wheel frame from rotating about itspivot connection.

The digging wheel 33 is rotatably supported by the wheel frame 25. Moreparticularly, the wheel 33 is mounted on a plurality of rollers 37,carried by a subframe 109 attached to the wheel frame 25, and the drivesprockets 38 which are suitably journalled in the wheel frame 25.

In operation, with the digging wheel 33 in its raised position and withthe ditcher either stationary or moving, the operator, actuates liftingcylinders 27 to extend together to lower the slide members 28 and thusto lower the forward end of the wheel frame 25. As the wheel 33commences its digging action in the ground, the operator causes the holddown cylinders 30 to extend, thus lowering the rearward end of the wheelframe 25 relative to its forward end and allowing the digging wheel 33to excavate deeper into the ground. As digging progresses, the operatorlowers the wheel 33 to obtain the desired depth of trench by alternatelyoperating cylinders 27 and 30. The independent operation of cylinders 27and 30 enables the operator to move wheel frame 25 into a horizontalposition, as depicted in FIG. 1. This permits the conveyor system 39 tooperate efficiently, since if the ditcher was operated with the wheelframe 25, and thus the conveyor 39, at an angle to the horizontal, theexcavated earth would tend to slide to one side or other of the conveyoras it was being removed.

The raising of the wheel assembly from the ground is a reverse of theabove procedure, with cylinders 27 and 30 being operated independentlyor together to effect the lifting motion.

The positioning of the wheel in the vertical sense, and thusly thecontrol of the digging depth, is accomplished by extending or retractingthe cylinders 27, cylinders 30 being extended or retracted in turn tomaintain the wheel frame 25 in a generally horizontal position.

The wheel frame locating elements facilitate the tilting of the wheel33. The tilting of the wheel frame 25, and its digging wheel 33, isaccomplished by the independent extension or retraction of one cylinder27 relative to the other cylinder 27; thus the wheel frame 25 is givenan angular displacment relative to the plane of the main frame 1. I

The upper cylinders 30 are not actuated in the tilting procedure andcannot be actuated independently one relative to the other. Thus whenthe wheel frame 25 is tilted, the pin member 41 on the relatively higherside of frame 25 will slide rearwards in its slot 40; the pin member 41on the relatively lower side of frame 25 will slide forwards in its slot40. If pin members 41 engaged closely-fitting circular holes in bracketmember 32, rather than slots, the tilting motion would only be possiblewith the independent operation of cylinders 30 relative one to the otheras well as the existing independent operation of cylinders 27. Thiswould eliminate the floating action which is provided by means of theslots. The advantages of the floating action are, as previouslydescribed:

l. To enable the angularity between the forward crawler section and therearward wheel section to exist to a minor degree so that smallundulations of the terrain are absorbed, thus providing a smoothbottomedtrench of constant depth.

2. To enable the wheel to rise slightly over non-ditchable objects atthe extreme lower area of the ditching depth.

The slots 40 allow the floating action with the wheel in its normaldigging position or in a tilted digging position.

When the wheel frame 25 is being raised or lowered and is not supporteddirectly by the ground, the pin members 41 slide to the extreme forwardends of the slots 40 due to the action of gravity upon the wheelassembly B and therefore the hold down cylinders 30 directly supportpart of the weight of the wheel assembly B and enable the raising orlowering action to proceed.

When the wheel assembly B is in a digging position, the pin members 41are positioned approximately halfway between the ends of the slots 40 toallow the floating action. In this position, the cylinders 30 exert adownward force through the pin members 51 on the wheel frame 25. Sincethe slots 40 are located rearwardly of the centre of the wheel 33, thisdownward force acts at a substantial leverage distance.

While a slot and sliding pin arrangement is shown, the invention is notto be limited to such a structure. Essentially, the slot 40 provides ashort slide for the end of the hold down cylinder 30. The same end couldbe achieved, for example, by substituting a slide rail having stop facesat each end and attaching the cylinder end to the rail. Alternatively,one could incorporate a free float control valve in the hydrauliccircuit controlling the cylinders 30. This latter system will permit thewheel to float, however it has a shortcoming in that in the floatposition the cylinders 30 will not maintain a positive hold down on thewheel frame.

Spherical bearings are provided at all points marked S (FIG. 1) to allowthe simultaneous angular and rotational movement necessary for theraising, lowering and tilting of the wheel frame. The angular movementis depicted in FIG. 5 and the rotational movement is depicted in FIG. 1.It will be understood that, while spherical bearings are preferred forthese connections, ball joints and other equivalents could also be used.

Track Width Adjust System This system is illustrated in FIG. 10. Firstand second transverse members 9 are part of the main frame 1. First andsecond sleeve members 11 are rigidly secured at the front and rear endsof the spaced, parallel, longitudinally extending track frames 90. Thetransverse members 9 extend into the sleeves 11 and can slide therein. Afirst pair of outwardly extending hydraulic cylinders 44 are eachconnected at their inner ends to the first transverse member at aboutits mid-point. At their outer ends, the first hydraulic cylinders areeach connected to one of the track frames above its longitudinal centreline. A second pair of outwardly extending hydraulic cylinders 44 areeach connected at their inner ends to the second transverse member atabout its midpoint. At their outer ends, each second hydraulic cylinderis connected to one of the track frames below its longitudinal centreline. Means for independently actuating each hydraulic cylinder areprovided, as described in the following discussion of the hydraulicsystems incorporated into the ditcher.

The track width adjust system used on this ditcher contains innovationswhich permit the mechanism to operate in a satisfactory manner. Firstly,referring to FIGS. 1 and 2, it is seen that there is an appreciabledistance L between the front and rear cylinder centre lines. Secondly,referring to FIG. 3, it is seen that there is an appreciable anglebetween the centre lines of the front and rear cylinders when viewedfrom the front. Thirdly, by means of the control valves in valve block43, the operator is able to control each cylinder 44 individually andseparately.

If there was only one control valve provided for the pair of front andrear cylinders 44 on each side, or one control valve for all fourcylinders 44, the system would not work. This is because the forcesresisting the action of each cylinder 44 are unequal due to varyingfriction between the sleeves 11 and transverse members 9, and unequaldistribution of the ditcher weight among the sliding members. Theseunequal forces would enable the cylinder pushing against the leastresistance to extend to the point at which the sleeves 11 were somisaligned on the transverse members 9 as to bind and resist furthermotion. At this point, the operator would be unable to complete thetrack adjustment. It is impossible to control these friction forces toobtain equal movment of both front and rear cylinders. Therefore it isdesirable to provide a separate control valve for each cylinder 44 theskewing and jamming tendencies of the sleeves ll require individuallycontrollable forces (provided by cylinders 44) to overcome them,although it would be possible to operate the system with one valvecontrolling the pair of cylinders either above or below the rack framecenterline.

The angle between the centerlines of the front and rear cylinders 44accomplishes two things. Firstly, the downward slope of the frontcylinders establishes a vertical force component which removes a part ofthe vertical supporting force from, and thereby reduces frictionbetween, sleeves 11 and transverse members 9. This reduces the lateralforce required to move the track assemblies outward. Secondly, aseparation in a vertical plane, denoted D in FIG. 3, is created betweenthe points of force application of the front and rear cylinders. Thisenables a couple to be created in a vertical plane by the alternateapplication of hydraulic pressure to the front and rear cylinders 44 inorder to reduce friction forces on the horizontal mating surfaces ofsleeves 11 and transverse members 9. Similarly, the longitudinalseparation of the cylinders enables a couple to be created in ahorizontal plane, which is effective in reducing the friction force onthe vertical mating surfaces of sleeves 9 and transverse members 11.

Hydraulic System The hydraulic system of the ditcher comprises threemain sub-systems:

A. Rear engine-driven duplex pump system.

B. Rear engine-driven pump-motor system.

C. Front engine-driven pump-motor system. A. Rear Engine-Driven DuplexPump System The duplex pump 22 powers all mechanism on the ditchingmachine which are actuated by hydraulic cylinders and are not incontinuous motion when the ditcher is in operation. The duplex pump 22also supplies pressure to the crawler brakes 49 and hoist 79. The duplexpump 22 is driven from the front crankshaft system of engine 13.

1. Forward, Smaller Section Of Duplex Pump 22 The operator, from withinthe operator compartment 42, and by manipulating four separate valves invalve block 43 (one for each cylinder 44) can actuate individually andindependently each track adjusting cylinder 44 and can shift the tracksinwardly or outwardly from the centerline of the ditcher by using thefront track adjusting cylinders and rear track adjusting cylindersalternately or together. To be able to move the tracks inwardly oroutwardly at all, the operator should be able to wiggle them byoperating each front and rear cylinder 44 individually.

Flow divider 45 is supplied with high pressure hydraulic fluid from theforward section of pump 22 through valve block 43. The flow divider isadjustable by the operator to supply high pressure hydraulic fluideither to valve block 48 or to hoist 79, but not to both at once. Hoist79 is normally used when the ditcher is stationary to assist in theinstallation or removal of buckets (FIG. 1), the raising of the conveyorextensions, and any work, to which the hoist,can reach, which requires aheavy lifting capability.

The operator, by means of a control valve in valve block 48 can selectthe low, digging ground speeds, the faster, transport ground speed orneutral by activating the hydraulic cylinders 46 which move shift forkswithin the travel gear boxes 47 to select the appropriate gear orneutral.

The operator, by means of a control valve in valve block 48 can applypressure to the brake units 49 embodied in each crawler final drivehousing, and also release said pressure. Another valve 50 is provided tohold pressure in the brake pressure apply lines and thereby to maintainthe brakes in the applied condition and so prevent the machine frommoving if it is stationed on a surface such as a hill on which it wouldmove wihtout the use of its own power.

Valve block 43, and (through flow divider 45) valve block 48 and hoist79 are supplied with hydraulic fluid under pressure from the forwardsmaller section of duplex pump 22, which draws fluid from the hydraulicreservoir tank 23 through the fluid supply line 51 and filter F3.Exhaust hydraulic fluid from the valve blocks 43 and 48 returns to thereservoir through two lines 67, filter F8 and main fluid return line 52.It is not an imperative feature that the four valves which independentlyoperate the crawler trackwidth adjust system be mounted together in thesame valve block 43. They can each be separate, in pairs, etc. The shiftcontrol valve and brake control valve which comprise valve block 48 canbe separate instead of being contained within the same valve block.

2. Rearward, Larger Section Of Duplex Pump 22 The rearward, largesection of the duplex pump 22 draws hydraulic fluid from the same supplyline as the forward, smaller section of the same pump, and suppliesfluid under pressure to valve block 53. The operator may, be operating avalve in valve block 53, extend or retract the upper cylinders 30, whichoperate equally and in parallel as described in previous sections. Thelength to which the two upper cylinders 30 are extended at any moment intime is maintained equally the same by the use of a flow divider 54which maintains equal fluid flow to and from each cylinder 30.

There is the possibility that the operator may at some time wish toapply individual and separate control to each hydraulic cylinder 30, forexample if he wishes to apply more downward force to one side of thedigging wheel than the other to compensate for irregularities in thematerial being trenched. This capability would be useful with respect todigging wheels wider than that used on the invention at the presenttime. The individual control of each cylinder 30 is accomplished byremoving flow divider 54 and installing lines 80, shown dashed in FIG.7, to connect the spare control valve which exists in valve block 53with one cylinder 30. The other cylinder 30 is then actuated by thecontrol valve in valve block 53 which is shown in FIG. 7 as supplyingflow divider 54.

Valve block 53 also incorporates two valves, one for each cylinder 27,by means of which the operator may extend or retract the two slidecylinders 27 independently and individualy, or together. The independentoperation of the two slide cylinders 27 enables the operator to adjustthe tilt of the digging wheel for digging on side hills, in which caseone cylinder 27 is extended more than the other cylinder 27 to createthe desired angle, as shown in FIG. 5.

The valves incorporated together in valve block 53 can each be mountedseparately or in pairs without effecting the operation of the hydrauliccylinders 27 and 30. Exhaust fluid from the hydraulic sustems controlledby valve block 53 is returned to the reservoir 23 through line 68,filter F8 and main fluid return line 52.

In the event that any part of the hydraulic circuits supplying hydraulicfluid to cylinders 27 and 30 should fail causing fluid to escape fromthe system to the atmosphere, automatic check valves 55 on each cylinder27 and 30 prevent displacement of the hydraulic fluid within thecylinders 27 and 30 and therefore prevent movement of the pistons in thecylinders. This is an important safety feature as it prevents thedigging wheel assembly from falling unexpectedly from the raisedposition and causing possible injury to workers.

It is not necessary to operate front engine 12 and pumps 17 to performany of the functions described in section A above, except as noted underCross-Over Systembelow.

B. Rear Engine-Driven Pump Motor System The rear engine 13 as previouslydescribed drives four variable-displacement pumps 21 by mechanicalmeans. The pump-motor systems described below are of hydrostatic type.

i. Conveyor Drive Pump-Motor System The forward pair ofvariable-displacement pumps 21 is connected each one to afixed-displacement hydraulic motor 61 by pressure lines 69. Thehydraulic motors 61 drive the conveyor mechanism which removes excavatedmaterial from the machine and deposits it on unexcavated terrain. Byadjusting the swashplate mechanism of the forward pair of pump 21remotely from within the compartment 42, the operator can adjust thespeed of the conveyor mechanism to match the amount of material beingexcavated and he can also, by means of the same control, reverse thesense of rotation of the motors 61 to permit the conveyor system todischarge the excavated material to either the left hand side or theright hand side of the trench. By adjusting the swashplate mechanism ofthe forward pair of pumps 21 to the neutral position so that no pumpingtakes place the operator can stop the conveyor mechanism when it is notrequired for example when the ditcher is moving under its own power toor from a work site and no ditching is being performed. The conveyorsystem would otherwise operate since the front pair of pumps 21 mustrotate when the crawler mechanism is operating due to the continuousmechanical connection between the pumps in gear box 20.

When the ditcher is being transported by means other than its own, it iscommon to separate the forward crawler portion of the ditcher from therearward digging wheel and its associated frame and mechanism to enablethe two portions to be transported separately. Since the pumps 21 are onthe forward crawler portion of the ditcher and the motors 61 are on therearward digging wheel assembly, the hydraulic lines 69 and 70 betweenthe pumps 21 and motors 61 can be separated by means of couplers 62without loss of hydrualic fluid.

The hydraulic lines from the forward pair of pumps 21 arecross-connected between the two high pressure lines and cross-connectedbetween the two lowpressure lines, this cross-connection being effectedby hoses 71 located just in front of couplers 62. The duplication ofpumps and circuits is a fail-safe feature so that if one pump shouldmalfunction, the other is able to drive the conveyor system at reducedspeed and trenching can proceed at a slower rate. This back-upcapability is of great importance from a standpoint of reliability inview of the difficult digging conditions likely to be encountered in theArctic and also in view of the maintenance and supply difficultiesassociated with the Artic, and which become critical with wintertimeoperation.

lt is necessary to be able to move the forward crawler portion of thetrencher by means of its own power, separate from the digging wheelassembly, when it is being manoeuvered for transportation to or fromwork sites. To accomplish this, the rear engine 13 must be running inorder that the rear pair of pumps 21 operate the crawler mechanism.However, the forward pair of pumps 21 must also operate if the rear pairof pumps are operating because of the continuous mechanical connectionbetween the pumps in gear box 20. The conveyor pump-motor circuits areincomplete since the hoses 69 and-70 have been separated at couplers 62in order to remove the digging wheel assembly. This means that the frontpair of pumps 21 would pump into lines which are closed and sealed atthe couplers 62. In this instance, extremely rapid pressure rise wouldcause failure through hydraulic lock in the front pumps 21 or the hosesconnected to them. To eliminate this possibility, automatic flow controlvalves 63, which are normally closed, open in order to complete thecircuit and permit the front pair of pumps 21 to rotate normally. It isnoted that it would be possible to operate the crawler mechanism withrear engine 13 running, and without the automatic flow control valves63, by placing the swashplate mechanisms of the forward pair of pumps 21(conveyor drive) in the exact neutral position so that no pumpingoccurred in these pumps. The automatic flow control valves 63 are asafety feature which ensures that no damage will occur if the operatorsswashplate control levers for the front pair of pumps are in anyposition other then neutral. p 2. Track-laying (Crawler Drive)Pump-Motor System The right-rear variable-displacement pump 2] drives afixed-displacement motor 64 which in turn drives, through the travelgear box 47, the track-laying (crawler) mechanism on the right-hand sideof the ditcher, and thereby propels the ditcher along the ground. Theleft-rear variable-displacement pump 21 drives a fixed-displacementmotor 64 which in the same manner drives the track-laying mechanism onthe lefthand side of the ditcher. The operator is able to steer theditcher by independently controlling the swashplate mechanisms of eachrear pump 21 and thereby speed up or slow down the trackmechanism on oneside relative to the other. The operator is also able to adjust theground speed of the ditcher and to cause the ditcher to move in either aforward or a rearward direction by operating the swashplate mechanism ofthe two rear pumps 21 in unison. He can also steer and adjust the speedof the ditcher by a combination of the abovementioned adjustments, andhe can also operate the ditching mechanism with the ditcher stationary,for example when beginning a trench, by adjusting the swashplatemechanisms of the two rear pumps 21 to neutral.

Common Features of the Conveyor Drive and Track-Laying Pump-MotorSystems Hydraulic fluid is provided from the main fluid supply line 51,through filters F4, F5, F6, and F7 to small charge pumps C on the endsof, and integral with all four pumps 21 to make up for leakage in theconveyor drive and track-laying (crawler drive) pump-motor systems.Leakage flow from the motors 61 and 64 is returned to pump cases 21means of free-flow (nonpressurized) lines and 72, and from the pumps 21to the reservoir 23 through lines 73 filter F8 and the main fluid returnline 52.

All four pumps 21 incorporate pressure relief valves to protect thehydraulic components from high pressures which would otherwise occur dueto possible overloading of the conveyor or track-drive mechanisms.

The swashplate mechanisms which enable the operator to vary the speed ofthe conveyor drive and crawler drive mechanisms also permit him toadjust the speed of engine 13 to any desired value up to maximum toobtain the best engine efficiency or power for the particular operatingconditions. The engine is then maintained at that speed by its governorcontrol. The adjustment of the swashplate mechanisms does not in itselfchange the rotational speed of engine 13.

It is not necessary to operate front engine 12 and pumps 17 to performany of the functions described in section B above, except as noted inCross-Over system below.

C. Front Engine-Driven Pump-Motor System The front engine 12 aspreviously described drives two variable-displacemnt hydraulic pumps 17by mechanical means. The flow from the two pumps 17 is delivered to acommon manifold 56 by separate lines 73 and thence by separate lines 74from the manifold 56 to the fixed-displacement digging wheel drivemotors 57. The manifold ensures a supply of hydraulic fluid of equalflow and equal pressure to each hydraulic motor 57, to equalize the loadcarried by each motor/Each motor 57 drives independently through a gearbox to a chain which ,turns the digging wheel 33 (FIG. 1) through thesprocket-segment gearing system. The four motors 57 are arranged two toeach side of the digging wheel. The return flow of hydraulic fluid frommotors 57 is through separate lines 75 to manifold 58 and is returned tothe low pressure side of the two pumps 17 by hoses 76. All hoses 75 and76 between the manifolds 56 and 58 and the hydraulic motors 57, and freeflow return lines 77, can be disconnected at motors 57 by means ofcouplers 66 without loss of hydraulic fluid. This facilitates theremoval of the rearward digging wheel portion of the ditcher from theforward crawler portion for transport purposes. This pump-motor systemis of hydrostatic type.

The duplication of pumps 17 and circuits is a fail-safe feature in thatif one pump should fail, the other is able to drive the digging wheel atreduced speed and trenching can proceed at a slower rate. Trenching isalso possible should one or two of the hydraulic motors 57 and- /ortheir associated circuits and drive mechanisms malfunction. This back-upcapability is of great importance from a reliability standpoint aspreviously discussed in section B.

Pressures which exceed the normal working pressures of this pump-motorsystem may be caused, for ex ample, when the digging wheel hitssomething extremely hard, causing the motors 57 to slow down or evenstall momentarily. To allow for this, and for any malfunction whichcould cause pressures to exist which exceed the operating limits of thecircuit, pressure relief valves 59 and one-way check valves 60 areprovided to divert the flow from pumps 17 in the direction from manifold56 to manifold 58 or vice-versa and thence back to the pumps. Thesevalves are in addition to pressure relief valves which are incorporatedin pumps 17. Pressure relief valves 59 are manually adjustable to enablethe maximum operating hydraulic pressure of the digging wheel drivepump-motor circuits to be varied over wide limits. This feature isuseful at intial start-up, for example, when the pressure relief settingis adjusted to a low value to enable the operation of the hydraulicpumps, motors, and digging wheel drive system to be checked with theleast risk of damage due to faculty hyraulic connections, etc. Theoperator may, by adjusting the relief valves, vary the maximum powerdeveloped by the motors 57 to suit any digging requirements.

Fluid is provided from the main fluid supply line 51 through filters F1and F2 to small charge pumps C on the ends of, and integral with, pumps17 to make up for leakage in the system. Leakage flow from the motors 57is returned to the pumps 17 by means of freeflow lines 77, and from thepumps 17 to the reservoir 23 through lines 78, filters F9 and F10 andthe main fluid return line 52.

It is desirable to be able to adjust the rotational speed of the diggingwheel 33 in fine increments without adjusting the rotational speed ofthe front engine 12. This is to enable front engine 12 to operate at apre-set optimum speed to obtain the best engine efficency and/or powerfor a particular operating condition. The engine is then maintained atthat speed by its governor control. The adjustment of the digging wheelspeed is accomplished by means of swashplate mechanisms incorporated inthe pumps 17 and which are remotely adjustable by the operator fromwithin the compartment 42 to provide a digging wheel speed infinitelyvariable between 0 and maximum. The swashplate mechanisms vary thedisplacement of the pumps 17 and therefore the amount of hydraulic fluiddelivered to the motors 57, thus directly varying the speed of themotors 57. The operator is able to adjust the swashplate mechanism ofthe pumps 17 individually as well as in unison, and therefore obtainvery fine control of digging wheel speed. By means of the swashplatemechanism the operator is also able to reverse the flow of fluid to themotors 57 and thereby reverse the rotation of the digging wheel ifnecessary. The adjustment of the swashplate mechanisms does not initself change the rotational speed of engine 12.

The functions performed by the hydraulic circuits described in section Cabove are not dependent on rear engine 13 and pumps 21. Motors 12 and 13power separate and different portions of the ditchers machinery, exceptas described in Cross-Over System below, and as such increase thereliability of the equipment.

C ross-Over System The basic feature of having two separate engines todrive the ditcher is utilized so that the front engine 12, in anemergency, can take over some of the functions of the rear engine 13. lnthe event that there occurs some malfunction in the rear engine 13, pumpdrive components 18, 19, 20, any of the pumps 21, or pump 22, it muststill be possible to lift the digging wheel out of the trench and movethe machine under its own power off of pipeline right-of-way to alocation where it can be repaired. This is extremely important in that astalled ditcher would halt the entire pipeline operation behind it, asituation which is undesirable from the standpoints of cost and time. Itis mandatory in such a situation that the stalled ditcher be movedquickly away from the right-of-way and another trencher take its place.

It is an object of the invention to incorporate a crossover system thatwould enable the front engine 12, through pumps 17, to power thetrack-laying (crawler drive) motors 64 and the various hydrauliccylinders 27, 30, 44, 46, and the crawler brakes 49 all these devicesbeing normally powered by rear engine 13 through the rear pair of pumps21 and duplex pump 22. The cross-over system is shown in FIG. 8 indashed lines.

To effect the cross-over, flow dividers 65 are operated to divert theflow in lines 73 and 76 from the motors 57 to the cross-over circuit. Toeffect thecrossover, it is also necessary to open the two valves 81,which are normally closed to prevent cross-connection between thedifferent hydraulic systems. It is necessary to isolate manifolds 56 and58 from pumps 17 by means of the flow dividers 65 since the output fromeach of the two pumps 17 must be independently adjustable by means ofthe swashplate mechanisms in order to steer the ditcher (see descriptionin section B, above, of crawler pump-motor system). With the cross-oversystem shown in FIG. 7, it is possible to operate all hydraulic deviceson the ditcher except the conveyor drive motors 61 and the digging wheeldrive motors 57.

It is noted that the plurality of hydraulic pumps used on the inventionis of great advantage because, in the event of a failure in part of somehydraulic circuit, any one of these pumps may be coupled relativelyconveniently, by means of flexible hoses and standardized fittings, topower a hydraulic device which is, in the normal operation of themachine, powered by some other hydraulic pump. This versatility of powerapplication and connection contributes to the overall reliability of themachine. Therefore, many cross-over hydraulic supply systems arepossible, in addition to the one described above and shown in FIG. 7.For example, in the event of a malfunction in the crawler drive pumps,conveyor drive pumps, or both, one or two pairs of lines 74 and 75 maybe disconnected from motors 57 to power the malfunctioning circuit.Output from pump 22 can also be diverted for the same purpose. In theseinstances, separate control valves and circuits for the lefthand andright-hand crawler brakes would be required for steering purposes.

Twin Double Segment Drive As shown in FIGS. 1, ll, 12, and 13, thedigging wheel assembly 33, incorporating the spaced rim assemblies 34,the double segment teeth assemblies 35, and buckets 36 is driven byengine 12 through a hydraulic-mechanical system.

Engine 12 drives hydraulic pumps 17 which in turn supply high-pressurehydraulic fluid to four hydraulic motors 57 mounted two on each side ofthe wheel frame 25. The motors 57 each drive a reduction gear box 82which in turn drives through chains 83 to the two shafts 84 and shaft85, supported by bearings 86. The double sprockets 38 are rigidlyattached to each shaft 84 and said sprockets 38 are rigidity attached toeach side of shaft 85. The sprockets 38 mesh with segments 35 and thuscause the wheel assembly 33 to rotate. One sprocket 38 of each pairmeshes with a segment row on the inner side of rim 34. The othersprocket 38 of each pair meshes with a segment row on the outer side ofrim 34 (FIG. 12). The smooth surfaces 88 (FIG. 13) of each sprocket 38located betweeen the gear tooth areas of each pair of sprockets bearsagainst the smooth inner surface of the segments 35 in similar fashionto rollers 37 (FIG. 1) and help to locate and support the wheel, as wellas relieving the gear teeth from stresses resulting from bearing theweight of the wheel.

Shaft 85 is driven by two motors 57 and is supported by two bearings 86mounted directly on wheel frame assembly 24. The two shafts 84, drivenby one motor 57 each, are supported at their outboard ends .by twobearings 86 mounted directly to frame assembly 24, and at their innerends by two bearings 86 mounted on support member 87 which is attachedto wheel frame assembly 24.

The shaft 85 drives to both rims 34 of wheel assembly 33 and thereforeprevents any relative rotation of the two rims which might occur if thedrive systems to the two sides were totally separate. Such relativerotation would impart a twisting stress to the buckets connecting thetwo rims; such stress cannot occur in this design.

Whereas the usual trencher designs employ one row of segments per rim,this invention employs two rows per rim (FIGs. l3, l4); and, instead ofone sprocket per row of segments, this invention employs two sprocketsper row of segments. Therefore, each segment row of this designtransmits only half the power transmitted by one row in previousdesigns; each sprocket transmits only one fourth the power transmittedby one sprocket in previous designs. This load-sharing, brought about bya multiplicity of segment rows and sprockets, contributes greatly to theoverall reliability which is an objective of this design.

What is claimed is:

1. In a ditcher comprising a carrier having a main frame, extendingsubstantially parallel to the ground surface, and an upstandingsuspension frame rigidly secured to said main frame, and

a rigid wheel frame, supporting a rotatable ditching wheel, pivotallyconnected at its front end to the suspension frame and movable thereonbetween a lowered position and an elevated position, and

means for raising and lowering the wheel frame between said positions,

the improvement which comprises a hold' down hydraulic cylinderpivotally connected at its front end to the suspension frame forrotation about an axis substantially parallel to the plane of the mainframe;

means slidably connecting the rear end portion of the hold down cylinderwith a portion of the wheel frame, said means comprising slide means,formed in one of the portions, having stop faces at each end of theslide means, and a connecting member joining the portions together,whereby the connecting member may move along the slide means between thelimiting stop faces; and

means for controllably actuating the hold down hydraulic cylinder toexpand or cotract it.

2. In a ditcher comprising a carrier having a main frame, extendingsubstantially parallel with the ground surface, and an upstandingsuspension frame rigidly secured to said main frame, and

a rigid wheel frame, supporting a rotatable ditching wheel, pivotallyconnected at its front end to the rear end of the suspension frame andmovable thereon between a lowered position and an elevated position, and

means for raising and lowering the wheel frame between said positions,

the improvement which comprises:

a hold down hydraulic cylinder positioned at an acute angle fromhorizontal and pivotally connected at its upper front end to thesuspension frame for rotation about an axis substantially parallel tothe plane of the main frame;

means for controllably actuating the hold down cylinder to expand orcontract it;

a member connected to the wheel frame, said member forming slide meansand having stop faces at each end of the slide means;

1. In a ditcher comprising a carrier having a main frame, extendingsubstantially parallel to the ground surface, and an upstandingsuspension frame rigidly secured to said main frame, and a rigid wheelframe, supporting a rotatable ditching wheel, pivotally connected at itsfront end to the suspension frame and movable thereon between a loweredposition and an elevated position, and means for raising and loweringthe wheel frame between said positions, the improvement which comprisesa hold down hydraulic cylinder pivotally connected at its front end tothe suspension frame for rotation about an axis substantially parallelto the plane of the main frame; means slidably connecting the rear endportion of the hold down cylinder with a portion of the wheel frame,said means comprising slide means, formed in one of the portions, havingstop faces at each end of the slide means, and a connecting memberjoining the portions together, whereby the connecting member may movealong the slide means between the limiting stop faces; and means forcontrollably actuating the hold down hydraulic cylinder to expand orcotract it.
 2. In a ditcher comprising a carrier having a main frame,extending substantially parallel with the ground surface, and anupstanding suspension frame rigidly secured to said main frame, and arigid wheel frame, supporting a rotatable ditching wheel, pivotallyconnected at its front end to the rear end of the suspension frame andmovable thereon between a lowered position and an elevated position, andmeans for raising and lowering the wheel frame between said positions,the improvement which comprises: a hold down hydraulic cylinderpositioned at an acute angle from horizontal and pivotally connected atits upper front end to the suspension frame for rotation about an axissubstantially parallel to the plane of the main frame; means forcontrollably actuating the hold down cylinder to expand or contract it;a member connected to the wheel frame, said member forming slide meansand having stop faces at each end of the slide means; and meansconnecting the lower rear end of the hold down cylinder to the memberand arranged to enable said cylinder end to travel along the slide meansbetween the stop faces; whereby the hold down cylinder and saidconnecting means may cooperate to constrain the wheel frame in thedigging position while permitting a limited range of movement by thewheel frame about its pivot connection with the suspension frame.
 3. Theimprovement as set forth in claim 2 wherein: the slide extendslongitudinally substantially parallel to the longitudinal axis of thewheel frame.
 4. In a ditcher comprising a carrier having a main frame,exTending substantially parallel with the ground surface, and anupstanding suspension frame rigidly secured to the main frame, a rigidwheel frame, supporting a rotatable ditching wheel, pivotally connectedat its front end to the rear end of the suspension frame and movablethereon between a lowered position and an elevated position, and ''meansfor raising and lowering the wheel frame between said positions, theimprovement which comprises: a member connected to the upper section ofthe wheel frame and having a slot formed therein said slot having endfaces and extending longitudinally substantially parallel to thelongitudinal axis of the wheel frame; a pin member disposed in the slottransversely thereof for sliding movement therealong; a hold downhydraulic cylinder pivotally connected at its front end to the upperportion of the suspension frame, for rotation about an axissubstantially parallel to the plane of the main frame, and at its rearend to the pin member whereby the cylinder''s rear end may travel alongthe slot between its end faces; whereby the member, pin member andcylinder may cooperate to constrain the wheel frame in the diggingposition while permitting a limited range of movement of the wheel frameabout is pivot connection with the suspension frame.
 5. In a ditchercomprising a carrier having a main frame extending substantiallyparallel with the ground surface, and an upstanding suspension framerigidly mounted on the main frame, and a rigid wheel frame, supporting arotatable ditching wheel, connected at its front end to the rear end ofthe suspension frame and movable thereon between a lowered position andan elevated position, the improvement which comprises: at least twospaced, parallel lifting members, adapted to be independently linearlycontracted or expanded between fully open and fully closed positions andlocked at any position intermediate said fully opened and closedpositions, each lifting member being connected at one end to thesuspension frame; first coupling means connecting the wheel frame toeach lifting member, whereby the wheel frame may be moved by the liftingmembers between the lowered and elevated positions, said first couplingmeans being adapted to permit of the wheel frame being tilted relativeto the plane of the main frame and rotated in a vertical plane about anaxis, substantially parallel with the ground whereby, when the liftingmembers are expanded or contracted to uneven lengths, the wheel frame istilted; at least one hold down member; second coupling means connectingthe front end of each hold down member to the upper end of thesuspension frame, said second coupling means being adapted to permit ofthe wheel frame being tilted relative to the plane of the main frame androtated in a vertical plane about an axis substantially parallel withthe ground; third coupling means connecting the rear end of each holddown member to the wheel frame, said third coupling means being adaptedto permit of the wheel frame being tilted relative to the plane of themain frame and rotated in a vertical plane about an axis substantiallyparallel with the ground surface; each said hold down member beingadapted to be linearly contracted or expanded between fully closed andfully open positions and locked at any position intermediate said fullyclosed and open positions, whereby, when actuated, said hold down membermay rotate the wheel frame in a vertical plane about the first couplingmeans to a desired position and, when locked, constrains the wheel frameto said desired position.
 6. The ditcher as set forth in claim 5comprising slide means, connecting the wheel frame and the thirdcoupling means, for permitting limited sliding motion of the rear end ofthe hold down member relative to the wheel frame.
 7. The ditcher as setforth in claim 5 comprising: a member connected to the upper section ofthe wheel frame and having a slot formed therein, Said slot having endfaces and extending longitudinally substantially parallel to thelongitudinal axis of the wheel frame; said third spherical bearing meanscomprising a pin member which is disposed in the slot transverselythereof for sliding movement therealong; whereby the hold down hydrauliccylinder, third spherical bearing means and member may cooperate toconstrain the wheel frame in the digging position while permitting alimited range of movement by the wheel frame about its pivot connectionwith the suspesnion frame.
 8. In a ditcher comprising a carrier having amain frame extending susbstantially parallel with the ground surface andan upstanding suspension frame rigidly mounted on the main frame, and arigid wheel frame supporting a rotatable ditching wheel pivotallyconnected at its front end to the rear end of the suspension frame andmovable thereon between a lowered position and an elevated position. theimprovement which comprises: at least two spaced, parallel, liftinghydraulic cylinders, adapted to be independently contracted or expanded,each said cylinder bearing being connected at its upper end to the upperportion of the suspension frame; slide members, slidably mounted on thesuspension frame, each slide member being attached to the lower end ofone of the lifting cylinders; first spherical bearing means connectingthe front end of the wheel frame with each of the slide members; secondspherical bearing means connecting each slide member with the lower endof one of the lifting cylinders; at least one hold down hydrauliccylinder; third spherical bearing means connecting the front end of eachhold down hydraulic cylinder to the upper portion of the suspensionframe; fourth spherical bearing means connecting the rear end of eachhold down hydraulic cylinder to the upper rear portion of the wheelframe; and means for controllably actuating the hydraulic cylinders toexpand or contract them; whereby the lifting hydraulic cylinders may beexpanded or contracted equally to lower or raise the wheel frame, andmay be expanded or contracted unequally to tilt the wheel frame relativeto the plane of the main frame, and the hold down hydraulic cylinder maybe actuated to rotate the wheel frame in a vertical plane about itspivot connection with the suspension frame.
 9. The improvement as setforth in claim 8 comprising: a member connected to the upper section ofthe wheel frame and having a slot formed therein, said slot having endfaces and extending longitudinally substantially parallel to thelongitudinal axis of the wheel frame; said fourth spherical bearingmeans comprising a pin member which is disposed in the slot transverselythereof for sliding movement therealong; whereby the hold down hydrauliccylinder, fourth spherical bearing means and member may cooperate toconstrain the wheel frame in the digging position while permitting alimited range of movement by the wheel frame about its pivot connectionwith the suspension frame.
 10. The improvement as set forth in claim 9wherein: the slot is positioned rearwardly of the longitudinal mid-pointof the wheel frame.